1. Field of the Invention
This invention relates to the use of a barrier to eliminate arcing between phases during operation of multiphase circuit breakers.
2. Description of the Related Art
Circuit breakers are widely used in residential and industrial applications for the interruption of electrical current upon overcurrent conditions caused by short circuits or by ground faults. In a multi-phase circuit, it is common to have the contact and blade assemblies of the circuit breaker for all phases mechanically linked to each other so that the tripping of any one of any phases will cause the other phases to trip, opening the contacts of all phases. A crossbar that is attached to the circuit breaker blades or mechanisms of a multi-mechanism breaker accomplishes this linkage, providing the necessary simultaneous opening of all phase contacts.
The requirement of having sufficient space in the assembly to allow motion of the crossbar means that there is an open area in the insulation between the phases of the individual breaker. During interruption of electric current, hot ionized electrically conductive gases are produced between the contacts of the individual phases. The ionized gases from one phase may mix with the ionized gases from an adjacent phase, leading to loss of electrical insulation integrity and resulting in arcing between the phases. This kind of catastrophic failure can potentially damage the circuit breaker and the equipment that the circuit breakers are designed to protect.
Phase barriers that fit loosely over the crossbar have been used to reduce the occurrence of cross-phase arcing. Current methods use adhesive sealants to attach the barriers to the crossbar. These adhesives can melt under normal operating conditions, degrading the mechanical integrity of the barrier. In addition, whenever a breaker is tripped, small amounts of carbon and metal particles are deposited on the crossbar, increasing the risk of over-surface dielectric breakdown, necessitating the use of a sealant. The sealant and adhesives represent health risks to personnel involved in the assembly process. The sealant and adhesive emit vapors that are toxic at levels that are unacceptable under EPA and OSHA regulations. To assemble typical phase barriers requires the construction of expensive air hoods to handle the toxic vapors for the protection of manufacturing personnel.
There is a need for a phase barrier that prevents mixing of ionized gases between phases, maintains through air dielectric integrity between phases, insures over-surface dielectric integrity of a crossbar and reduces or eliminates the emission of toxic vapors. Such a phase barrier should maintain the physical integrity of the barrier under normal operating conditions.